Transcription factor Erg regulates angiogenesis and endothelial apoptosis through VE-cadherin. Blood. 2008;111:3498-3506. [PMID: 18195090 DOI: 10.1182/blood-2007-08-105346]

The transcription factor Erg controls endothelial cell quiescence by repressing activity of nuclear factor (NF)-κB p65

The interaction of transcription factors with specific DNA sequences is critical for activation of gene expression programs. In endothelial cells (EC), the transcription factor NF-κB is important in the switch from quiescence to activation, and is tightly controlled to avoid excessive inflammation and organ damage. Here we describe a novel mechanism that controls the activation of NF-κB in EC. The transcription factor Erg, the most highly expressed ETS member in resting EC, controls quiescence by repressing proinflammatory gene expression. Focusing on intercellular adhesion molecule 1(ICAM)-1 as a model, we identify two ETS binding sites (EBS −118 and −181) within the ICAM-1 promoter required for Erg-mediated repression. We show that Erg binds to both EBS −118 and EBS −181, the latter located within the NF-κB binding site. Interestingly, inhibition of Erg expression in quiescent EC results in increased NF-κB-dependent ICAM-1 expression, indicating that Erg represses basal NF-κB activity. Erg prevents NF-κB p65 from binding to the ICAM-1 promoter, suggesting a direct mechanism of interference. Gene set enrichment analysis of transcriptome profiles of Erg and NF-κB-dependent genes, together with chromatin immunoprecipitation (ChIP) studies, reveals that this mechanism is common to other proinflammatory genes, including cIAP-2 and IL-8. These results identify a role for Erg as a gatekeeper controlling vascular inflammation, thus providing an important barrier to protect against inappropriate endothelial activation.

Clinical potential of the ERG oncoprotein in prostate cancer

Oncogenic activation of ERG resulting from gene fusion is present in over half of all patients with prostate cancer in Western countries. Although the underlying genetic mechanisms have been extensively studied, evaluation of the ERG oncoprotein--the translational product of ERG gene fusions--has just begun. The robust correlation between ERG oncoprotein detection and gene fusion status enables rapid characterization of this protein in large patient cohorts. Recent studies have focused on characterizing the ERG oncoprotein and determining its potential role in the diagnosis and biological stratification of prostate cancer.

The transcription factor Erg regulates expression of histone deacetylase 6 and multiple pathways involved in endothelial cell migration and angiogenesis

The endothelial ETS transcription factor Erg plays an important role in homeostasis and angiogenesis by regulating many endothelial functions including survival and junction stability. Here we show that Erg regulates endothelial cell (EC) migration. Transcriptome profiling of Erg-deficient ECs identified ∼ 80 genes involved in cell migration as candidate Erg targets, including many regulators of Rho- GTPases. Inhibition of Erg expression in HUVECs resulted in decreased migration in vitro, while Erg overexpression using adenovirus caused increased migration. Live-cell imaging of Erg-deficient HUVECs showed a reduction in lamellipodia, in line with decreased motility. Both actin and tubulin cytoskeletons were disrupted in Erg-deficient ECs, with a dramatic increase in tubulin acetylation. Among the most significant microarray hits was the cytosolic histone deacetylase 6 (HDAC6), a regulator of cell migration. Chromatin immunoprecipitation (ChIP) and transactivation studies demonstrated that Erg regulates HDAC6 expression. Rescue experiments confirmed that HDAC6 mediates the Erg-dependent regulation of tubulin acetylation and actin localization. In vivo, inhibition of Erg expression in angiogenic ECs resulted in decreased HDAC6 expression with increased tubulin acetylation. Thus, we have identified a novel function for the transcription factor Erg in regulating HDAC6 and multiple pathways essential for EC migration and angiogenesis.

ETS-related gene (ERG) controls endothelial cell permeability via transcriptional regulation of the claudin 5 (CLDN5) gene

ETS-related gene (ERG) is a member of the ETS transcription factor family. Our previous studies have shown that ERG expression is highly enriched in endothelial cells (EC) both in vitro and in vivo. ERG expression is markedly repressed in response to inflammatory stimuli. It has been shown that ERG is a positive regulator of several EC-restricted genes including VE-cadherin, endoglin, and von Willebrand factor, and a negative regulator of other genes such as interleukin (IL)-8 and intercellular adhesion molecule (ICAM)-1. In this study we have identified a novel role for ERG in the regulation of EC barrier function. ERG knockdown results in marked increases in EC permeability. This is associated with a significant increase of stress fiber and gap formation in EC. Furthermore, we identify CLDN5 as a downstream target of ERG in EC. Thus, our results suggest that ERG plays a pivotal role in regulating EC barrier function and that this effect is mediated in part through its regulation of CLDN5 gene expression.

Prostate cancer as a model system for genetic diversity in tumors

This chapter will summarize novel understandings of the early molecular events in prostatic carcinogenesis that may underlie both the genetic and clinical heterogeneity. Areas covered include preneoplasia, stem cell concepts, telomere abnormalities, and the nature of tumor-stromal interactions. The oncogenomics of prostate cancer is reviewed with emphasis on androgen signaling, ETS gene family aberrations, and PTEN deletion. The notion that "field cancerization," coupled with genomic instability may explain both the occurrence of multifocal disease, and the recent observations of genetic diversity of ERG alteration in individual tumors are discussed. Collectively, genomic studies are rapidly moving human prostate cancer closer to the promise of personalized medicine, so that specific genetic profiles of individual tumors will determine the best therapeutic approaches.

Oncogenic activation of ERG: A predominant mechanism in prostate cancer

Prevalent gene fusions involving regulatory sequences of the androgen receptor (AR) regulated genes (primarily TMPRSS2) and protein coding sequences of nuclear transcription factors of the ETS gene family (predominantly ERG) result in unscheduled androgen dependent ERG expression in prostate cancer (CaP).Cumulative data from a large number of studies in the past six years accentuate ERG alterations in more than half of all CaP patients in Western countries. Studies underscore that ERG functions are involved in the biology of CaP. ERG expression in normal context is selective to endothelial cells, specific hematopoetic cells and pre-cartilage cells. Normal functions of ERG are highlighted in hematopoetic stem cells. Emerging data continues to unravel molecular and cellular mechanisms by which ERG may contribute to CaP. Herein, we focus on biological and clinical aspects of ERG oncogenic alterations, potential of ERG-based stratification of CaP and the possibilities of targeting the ERG network in developing new therapeutic strategies for the disease.

[Biological functions of the duplicated GGAA-motifs in various human promoter regions]

Transcription is one of the most fundamental cellular functions and is an enzyme-complex mediated reaction that converts DNA sequences into mRNA. TATA-box is known to be an important motif for transcription. However, there are majority of promoters that have no TATA-box. They are called as TATA-less promoters and possess other elements that determine the transcription start site (TSS) of the genes. Multiple protein factors including ETS family proteins are known to recognize and bind to the GGAA containing sequences. In addition, it has been reported that the ETS binding motifs play important roles in regulation of various promoters. Here, we propose that the duplication and multiplication of the GGAA motifs are responsible for the initiation of transcription from TATA-less promoters.

ERG deregulation induces PIM1 over-expression and aneuploidy in prostate epithelial cells

The ERG gene belongs to the ETS family of transcription factors and has been found to be involved in atypical chromosomal rearrangements in several cancers. To gain insight into the oncogenic activity of ERG, we compared the gene expression profile of NIH-3T3 cells stably expressing the coding regions of the three main ERG oncogenic fusions: TMPRSS2/ERG (tERG), EWS/ERG and FUS/ERG. We found that all three ERG fusions significantly up-regulate PIM1 expression in the NIH-3T3 cell line. PIM1 is a serine/threonine kinase frequently over-expressed in cancers of haematological and epithelial origin. We show here that tERG expression induces PIM1 in the non-malignant prostate cell line RWPE-1, strengthening the relation between tERG and PIM1 up-regulation in the initial stages of prostate carcinogenesis. Silencing of tERG reversed PIM1 induction. A significant association between ERG and PIM1 expression in clinical prostate carcinoma specimens was found, suggesting that such a mechanism may be relevant in vivo. Chromatin Immunoprecipitation experiments showed that tERG directly binds to PIM1 promoter in the RWPE-1 prostate cell line, suggesting that tERG could be a direct regulator of PIM1 expression. The up-regulation of PIM1 induced by tERG over-expression significantly modified Cyclin B1 levels and increased the percentage of aneuploid cells in the RWPE-1 cell line after taxane-based treatment. Here we provide the first evidence for an ERG-mediated PIM1 up-regulation in prostate cells in vitro and in vivo, suggesting a direct effect of ERG transcriptional activity in the alteration of genetic stability.

Vascular endothelial cadherin modulates renal interstitial fibrosis

BACKGROUND/AIMS

Renal interstitial fibrosis is a final common pathway of all chronic, progressive kidney diseases. Peritubular capillary rarefaction is strongly correlated with fibrosis. The adherens junction protein vascular endothelial cadherin (VE-cadherin) is thought to play a critical role in vascular integrity. We hypothesized that VE-cadherin modulates the renal microcirculation during fibrogenesis and ultimately affects renal fibrosis.

METHODS

Unilateral ureteral obstruction (UUO) was used as a renal fibrosis model in VE-cadherin heterozygote (VE+/-) and wild-type (WT) mice, and the kidneys were harvested at days 3, 7, and 14. Peritubular capillary changes and fibrogenesis were investigated.

RESULTS

VE+/- mice had lower levels of VE-cadherin protein than WT mice at 3 and 7, but not 14 days after UUO. Vascular permeability was significantly greater in VE+/- mice 7 days after UUO, while peritubular capillary density was not significantly different in VE+/- and WT mice. Interstitial myofibroblast numbers and collagen I and III mRNA levels were significantly higher in VE+/- mice, consistent with a stronger early fibrogenic response. Expression of the pericyte marker neuron-glial antigen 2 was upregulated after UUO, but was not greater in VE+/- mice compared to the WT mice.

CONCLUSION

Our data suggest that VE-cadherin controls vascular permeability and limits fibrogenesis after UUO.

Regulation of endothelial cell development by ETS transcription factors

The ETS family of transcription factors plays an essential role in controlling endothelial gene expression. Multiple members of the ETS family are expressed in the developing endothelium and evidence suggests that the proteins function, to some extent, redundantly. However, recent studies have demonstrated a crucial non-redundant role for ETV2, as a primary player in specification and differentiation of the endothelial lineage. Here, we review the contribution of ETS factors, and their partner proteins, to the regulation of embryonic vascular development.

The oncogenic gene fusion TMPRSS2: ERG is not a diagnostic or prognostic marker for ovarian cancer

TMPRSS2:ERG is a gene fusion resulting from the chromosomal rearrangement of the androgen-regulated TMPRSS2 gene and the ETS transcription factor ERG, leading to the over-expression of the oncogenic molecule ERG. This gene rearrangement has been found in approximately half of all prostate cancers and ERG overexpression is considered as a novel diagnostic marker for prostate carcinoma. However, little is known about the role of the TMPRSS2:ERG gene fusion in ovarian cancer. The purpose of this study was to test ERG expression in ovarian cancer and its potential as a diagnostic marker for ovarian carcinoma progression. A tissue microarray containing 180 ovarian cancer tissues of various pathological types and grades were examined by immunohistochemical analysis for expression of ERG. We also used 40 prostate carcinoma tissues and 40 normal tissues for comparison in parallel experiments. ERG-positive expression was detected in 40% of the prostate tumor cancer, as well as in internal positive control endothelial cells, confirming over-expression of ERG in prostate cancer at relatively the same rate observed by others. In contrast, all of the ovarian tumor patient tissues of varying histologic types were ERG-negative, despite some positivity in endothelial cells. These results suggest that the oncogenic gene fusion TMPRSS2:ERG does not occur in ovarian cancer relative to prostate cancer. Therefore, development of ERG expression profile would not be a useful diagnostic or prognostic marker for ovarian cancer patient screening.

Key transcriptional regulators of early vascular development

The formation of the vasculature depends on the precise spatial and temporal control of gene expression to define endothelial cell identity and to ensure the correct distribution and structure of the forming vessel network. This review provides an overview of the establishment of the vascular system, accompanied by a detailed discussion of the transcription factors involved in regulating endothelial gene expression during vasculogenesis and early vessel formation in both fish and mammalian systems. We also review the transcriptional pathways lying both upstream and downstream of key vascular transcription factors.

Design of "smart" probes for optical imaging of apoptosis

Apoptosis is a mode of programmed cell death in multicellular organisms and plays a central role in controlling embryonic development, growth and differentiation and monitoring the induction of tumor cell death through anticancer therapy. Since the most effective chemotherapeutics rely on apoptosis, imaging apoptotic processes can be an invaluable tool to monitor therapeutic intervention and discover new drugs modulating apoptosis. The most attractive target for developing specific apoptosis imaging probes is caspases, crucial mediators of apoptosis. Up to now, various optical imaging strategies for apoptosis have been developed as an easy and economical modality. However, current optical applications are limited by poor sensitivity and specificity. A subset of molecular imaging contrast agents known as "activatable" or "smart" molecular probes allow for very high signal-to-background ratios compared to conventional targeted contrast agents and open up the possibility of imaging intracellular targets. In this review, we will discuss the unique design strategies and applications of activatable probes recently developed for fluorescence and bioluminescence imaging of caspase activity.

ERG gene rearrangement status in prostate cancer detected by immunohistochemistry

TMPRSS2-ERG, the most common gene fusion in prostate cancer, is associated with expression of a truncated protein product of the oncogene ERG. A novel anti-ERG monoclonal antibody has been recently characterized. We investigated the correlation between ERG rearrangement assessed by fluorescence in situ hybridization (FISH) and ERG expression detected by immunohistochemistry in a large cohort of patients treated with radical prostatectomy for clinically localized prostate cancer. Thirteen tissue microarrays comprising 305 tumors and a subset of 112 samples of nonneoplastic prostatic tissue were assessed for ERG rearrangement status by FISH and for ERG expression by immunohistochemistry. Accuracy of ERG detection by immunohistochemistry in predicting ERG status as assessed by FISH (criterion standard) was calculated in terms of sensitivity, specificity, positive and negative predictive values. Of 305 tumor foci, 103 (34%) showed ERG rearrangement by FISH. ERG was detected by immunohistochemistry in 100 (33%) cases, 99 of which were FISH positive. ERG detection by immunohistochemistry demonstrated a sensitivity and specificity of 96% and 99%, respectively, with positive and negative predictive values of 99% and 98%, respectively. None of the 112 samples of nonneoplastic prostatic tissue was rearranged by FISH or showed any ERG expression. In conclusion, ERG detection by immunohistochemistry in prostate cancer was highly predictive of ERG rearrangement as assessed by FISH in a large cohort of prostatectomy patients. Given the high yield and the easier task of performing immunohistochemistry vs. FISH, ERG assessment by immunohistochemistry may be useful for characterizing ERG status in prostate cancer.

Acute myeloid leukemia: a central role for the ETS factor ERG

Acute myeloid leukemia is a cancer of the myeloid lineage, characterized by the rapid proliferation of immature progenitor cells which accumulate in the bone marrow and interfere with the production of normal blood cells. Aberrant regulation of E-twenty-six (ETS) specific transcription factors such as PU.1 (SPI1) is thought to play a major role in this type of leukemia. The importance of these factors in normal blood development is highlighted by the fact that numerous studies showed a direct link between hematopoietic defects and aberrant regulation of ETS factor expression or expression of mutant forms. Apart from PU.1, another ETS factor, ERG, has emerged as a key player in normal hematopoiesis. Here, the role of this protein in normal and aberrant blood development will be discussed as well as the possibilities to therapeutically target this ETS factor.

RhoJ is an endothelial cell-restricted Rho GTPase that mediates vascular morphogenesis and is regulated by the transcription factor ERG

ERG is a member of the ETS transcription factor family that is highly enriched in endothelial cells (ECs). To further define the role of ERG in regulating EC function, we evaluated the effect of ERG knock-down on EC lumen formation in 3D collagen matrices. Blockade of ERG using siRNA completely interferes with EC lumen formation. Quantitative PCR (QPCR) was used to identify potential downstream gene targets of ERG. In particular, we identified RhoJ as the Rho GTPase family member that is closely related to Cdc42 as a target of ERG. Knockdown of ERG expression in ECs led to a 75% reduction in the expression of RhoJ. Chromatin immunoprecipitation and transactivation studies demonstrated that ERG could bind to functional sites in the proximal promoter of the RhoJ gene. Knock-down of RhoJ similarly resulted in a marked reduction in the ability of ECs to form lumens. Suppression of either ERG or RhoJ during EC lumen formation was associated with a marked increase in RhoA activation and a decrease in Rac1 and Cdc42 activation and their downstream effectors. Finally, in contrast to other Rho GTPases, RhoJ exhibits a highly EC-restricted expression pattern in several different tissues, including the brain, heart, lung, and liver.

The ERGonomics of hematopoietic stem cell self-renewal

Stem cells make more of themselves by self-renewing cell divisions. In the February 1, 2011, issue of Genes & Development, Taoudi and colleagues (pp. 251-262) show an essential role for the ETS transcription factor ERG in the self-renewal of embryonic hematopoietic stem cells. A model is presented in which the redundant functions of GATA2 and RUNX1 in self-renewal are under direct control of ERG.

Histone deacetylase inhibitors, valproic acid and trichostatin-A induce apoptosis and affect acetylation status of p53 in ERG-positive prostate cancer cells

An ETS family member, ETS Related Gene (ERG) is involved in the Ewing family of tumors as well as leukemias. Rearrangement of the ERG gene with the TMPRSS2 gene has been identified in the majority of prostate cancer patients. Additionally, overexpression of ERG is associated with unfavorable prognosis in prostate cancer patients similar to leukemia patients. Histone acetyltransferases (HATs) and histone deacetylases (HDACs) regulate transcription as well as epigenetic status of genes through acetylation of both histones and transcription factors. Deregulation of HATs and HDACs is frequently seen in various cancers, including prostate cancer. Many cellular oncogenes as well as tumor viral proteins are known to target either or both HATs and HDACs. Several studies have demonstrated that there are alterations of HDAC activity in prostate cancer cells. Recently, we found that ERG binds and inhibits HATs, which suggests that ERG is involved in deregulation of protein acetylation. Additionally, it has been shown that ERG is associated with a higher expression of HDACs. In this study, we tested the effect of the HDAC inhibitors valproic acid (VPA) and trichostatin-A (TSA) on ERG-positive prostate cancer cells (VCaP). We found that VPA and TSA induce apoptosis, upregulate p21/Waf1/CIP1, repress TMPRSS2-ERG expression and affect acetylation status of p53 in VCaP cells. These results suggest that HDAC inhibitors might restore HAT activity through two different ways: by inhibiting HDAC activity and by repressing HAT targeting oncoproteins such as ERG.

The possible functions of duplicated ets (GGAA) motifs located near transcription start sites of various human genes

Transcription is one of the most fundamental nuclear functions and is an enzyme complex-mediated reaction that converts DNA sequences into mRNA. Analyzing DNA sequences of 5′-flanking regions of several human genes that respond to 12-O-tetradecanoyl-phorbol-13-acetate (TPA) in HL-60 cells, we have identified that the ets (GGAA) motifs are duplicated, overlapped, or clustered within a 500-bp distance from the most 5′-upstream region of the cDNA. Multiple protein factors including Ets family proteins are known to recognize and bind to the GGAA containing sequences. In addition, it has been reported that the ets motifs play important roles in regulation of various promoters. Here, we propose a molecular mechanism, defined by the presence of duplication and multiplication of the GGAA motifs, that is responsible for the initiation of transcription of several genes and for the recruitment of binding proteins to the transcription start site (TSS) of TATA-less promoters.

ERG transcription factor as an immunohistochemical marker for vascular endothelial tumors and prostatic carcinoma

ERG, an ETS family transcription factor, is known to be expressed in endothelial cells, and oncogenic ERG gene fusions occur in subsets of prostatic carcinoma, acute myeloid leukemia, and Ewing sarcoma. In this study, we immunohistochemically investigated nuclear ERG expression using a new monoclonal antibody, CPDR ERG-MAb, that is highly specific for detecting ERG protein and ERG-expressing prostate carcinomas. A broad range of vascular endothelial (n = 250), other mesenchymal (n = 973), and epithelial tumors (n = 657) was examined to determine the use of ERG immunohistochemistry in surgical pathology. Only immunostains with ERG-positive normal endothelia (internal control) were considered valid, and only nuclear staining was considered to be positive. In adult tissues, ERG was restricted to endothelial cells and to a subset of bone marrow precursors, but early fetal mesenchyme and subpopulations of fetal cartilage were also positive. In vascular tumors, ERG was expressed in endothelia of all hemangiomas and lymphangiomas, and typically extensively expressed in 96 of 100 angiosarcomas, 42 of 43 epithelioid hemangioendotheliomas, and all 26 Kaposi sarcomas. Among nonvascular mesenchymal tumors, only blastic extramedullary myeloid tumors (7 of 10) and rare Ewing sarcomas (2 of 29) were positive. Among epithelial tumors, 30 of 66 prostatic adenocarcinomas showed focal-to-extensive ERG positivity, with no immunoreactivity in the normal prostate. Other carcinomas and epithelial tumors (n = 643) were ERG negative, with the exception of 1 of 42 large cell undifferentiated pulmonary carcinomas and 1 of 27 mesotheliomas, each of which showed focal nuclear ERG positivity. On the basis of the above observations, ERG is a highly specific new marker for benign and malignant vascular tumors. Among epithelial tumors, ERG shows a great promise as a marker to identify prostatic carcinoma in both primary and metastatic settings.

ERG dependence distinguishes developmental control of hematopoietic stem cell maintenance from hematopoietic specification

Although many genes are known to be critical for early hematopoiesis in the embryo, it remains unclear whether distinct regulatory pathways exist to control hematopoietic specification versus hematopoietic stem cell (HSC) emergence and function. Due to their interaction with key regulators of hematopoietic commitment, particular interest has focused on the role of the ETS family of transcription factors; of these, ERG is predicted to play an important role in the initiation of hematopoiesis, yet we do not know if or when ERG is required. Using in vitro and in vivo models of hematopoiesis and HSC development, we provide strong evidence that ERG is at the center of a distinct regulatory program that is not required for hematopoietic specification or differentiation but is critical for HSC maintenance during embryonic development. We show that, from the fetal period, ERG acts as a direct upstream regulator of Gata2 and Runx1 gene activity. Without ERG, physiological HSC maintenance fails, leading to the rapid exhaustion of definitive hematopoiesis.

Genome-wide screen reveals WNT11, a non-canonical WNT gene, as a direct target of ETS transcription factor ERG

E26 transforming sequence-related gene (ERG) is a transcription factor involved in normal hematopoiesis and is dysregulated in leukemia. ERG mRNA overexpression was associated with poor prognosis in a subset of patients with T-cell acute lymphoblastic leukemia (T-ALL) and acute myeloid leukemia (AML). Herein, a genome-wide screen of ERG target genes was conducted by chromatin immunoprecipitation-on-chip (ChIP-chip) in Jurkat cells. In this screen, 342 significant annotated genes were derived from this global approach. Notably, ERG-enriched targets included WNT signaling genes: WNT11, WNT2, WNT9A, CCND1 and FZD7. Furthermore, chromatin immunoprecipitation (ChIP) of normal and primary leukemia bone marrow material also confirmed WNT11 as a target of ERG in six of seven patient samples. A larger sampling of patient diagnostic material revealed that ERG and WNT11 mRNA were co-expressed in 80% of AML (n=30) and 40% in T-ALL (n=30) bone marrow samples. Small interfering RNA (siRNA)-mediated knockdown of ERG confirmed downregulation of WNT11 transcripts. Conversely, in a tet-on ERG-inducible assay, WNT11 transcripts were co-stimulated. A WNT pathway agonist, 6-bromoindirubin-3-oxime (BIO), was used to determine the effect of cell growth on the ERG-inducible cells. The addition of BIO resulted in an ERG-dependent proliferative growth advantage over ERG-uninduced cells. Finally, ERG induction prompted morphological transformation whereby round unpolarized K562 cells developed elongated protrusions and became polarized. This morphological transformation could effectively be inhibited with BIO and with siRNA knockdown of WNT11. In conclusion, ERG transcriptional networks in leukemia converge on WNT signaling targets. Specifically, WNT11 emerged as a direct target of ERG. Potent ERG induction promoted morphological transformation through WNT11 signals. The findings in this study unravel new ERG-directed molecular signals that may contribute to the resistance of current therapies in acute leukemia patients with poor prognosis characterized by high ERG mRNA expression.

Zebrafish as a model for hemorrhagic stroke

Blood vessels perform the fundamental role of providing conduits for the circulation of oxygen and nutrients and the removal of waste products throughout the body. Disruption of tissue perfusion by ischemia or hemorrhage of blood vessels has a range of devastating consequences including stroke. Stroke is a complex trait that includes both genetic and environmental risk factors. The zebrafish is an attractive model for the study of hemorrhagic stroke due to the conservation of the molecular mechanisms of blood vascular development among vertebrates and the experimental advantages that can be applied to zebrafish embryos and larva. This chapter will focus on the maintenance of vascular integrity and some of the seminal experimentation carried out in the zebrafish.

Fibromodulin suppresses nuclear factor-kappaB activity by inducing the delayed degradation of IKBA via a JNK-dependent pathway coupled to fibroblast apoptosis

Fibulin-5 (FBLN5) belongs to the Fibulin family of secreted extracellular matrix proteins, and our laboratory first established FBLN5 as a novel target for TGF-β in fibroblasts and endothelial cells. To better understand the pathophysiology of FBLN5, we carried out microarray analysis to identify fibroblast genes whose expressions were regulated by FBLN5 and TGF-β. In doing so, we identified fibromodulin (Fmod) as a novel target gene of FBLN5, and we validated the differential expression of Fmod and 12 other FBLN5-regulated genes by semi-quantitative real time PCR. Fmod belongs to the small leucine-rich family of proteoglycans, which are important constituents of mammalian extracellular matrices. Interestingly, parental 3T3-L1 fibroblasts displayed high levels of nuclear factor-κB (NF-κB) activity, although those engineered to express Fmod constitutively exhibited significantly reduced NF-κB activity, suggesting that Fmod functions to inhibit NF-κB signaling. By monitoring alterations in the activation of NF-κB and the degradation of its inhibitor, IκBα, we demonstrate for the first time that Fmod contributes to the constitutive degradation of IκBα protein in 3T3-L1 fibroblasts. Mechanistically, we observed Fmod to delay the degradation of IκBα by promoting the following: (i) activation of c-Jun N-terminal kinase; (ii) inhibition of calpain and casein kinase 2 activity; and (iii) induction of fibroblast apoptosis. Taken together, our study identified a novel function for Fmod in directing extracellular signaling, particularly the regulation of NF-κB activity and cell survival.

Endothelial von Willebrand factor regulates angiogenesis

The regulation of blood vessel formation is of fundamental importance to many physiological processes, and angiogenesis is a major area for novel therapeutic approaches to diseases from ischemia to cancer. A poorly understood clinical manifestation of pathological angiogenesis is angiodysplasia, vascular malformations that cause severe gastrointestinal bleeding. Angiodysplasia can be associated with von Willebrand disease (VWD), the most common bleeding disorder in man. VWD is caused by a defect or deficiency in von Willebrand factor (VWF), a glycoprotein essential for normal hemostasis that is involved in inflammation. We hypothesized that VWF regulates angiogenesis. Inhibition of VWF expression by short interfering RNA (siRNA) in endothelial cells (ECs) caused increased in vitro angiogenesis and increased vascular endothelial growth factor (VEGF) receptor-2 (VEGFR-2)-dependent proliferation and migration, coupled to decreased integrin αvβ3 levels and increased angiopoietin (Ang)-2 release. ECs expanded from blood-derived endothelial progenitor cells of VWD patients confirmed these results. Finally, 2 different approaches, in situ and in vivo, showed increased vascularization in VWF-deficient mice. We therefore identify a new function of VWF in ECs, which confirms VWF as a protein with multiple vascular roles and defines a novel link between hemostasis and angiogenesis. These results may have important consequences for the management of VWD, with potential therapeutic implications for vascular diseases.

Ets family protein, erg expression in developing and adult mouse tissues by a highly specific monoclonal antibody

Oncogenic activation of the ETS Related Gene (ERG) in humans was originally identified in subsets of Ewing sarcomas, myeloid leukemias and, recently, in the majority of prostate cancers. Expression of human ERG protein and consequently its functions in normal and disease states needs to be better understood in light of its suggested role in cell differentiation and proliferation. Here, we analyzed temporal and spatial expression of the Erg (mouse protein) by immunohistochemical analysis during mouse embryonic and adult organogenesis using a highly specific ERG monoclonal antibody (ERG MAb). This study establishes widespread immunolocalization of Erg protein in endothelial cells and restricted expression in precartilage and hematopoietic tissues. Intriguingly, Erg is not expressed in any epithelial tissue including prostate epithelium, or in infiltrating lymphocytes that are occasionally seen in the prostate environment, a common site of tumors with ERG rearrangements and unscheduled ERG expression. These findings will further aid in investigations of Erg functions in normal and disease conditions.

The transcription factor Erg inhibits vascular inflammation by repressing NF-kappaB activation and proinflammatory gene expression in endothelial cells

OBJECTIVE

To test whether ETS-related gene (Erg) inhibits tumor necrosis factor (TNF)-α-dependent endothelial activation and inflammation.

METHODS AND RESULTS

Endothelial activation underlies many vascular diseases, including atherosclerosis. Endothelial activation by proinflammatory cytokines decreases expression of the ETS transcription factor Erg. By using human umbilical vein endothelial cells (HUVECs), we showed that Erg overexpression by adenovirus (AdErg) repressed basal and TNF-α-induced expression of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule (VCAM), and interleukin 8 (IL-8). Erg inhibited TNF-α-dependent activation of the ICAM-1 promoter, nuclear factor (NF)-κB activity, and NF-κB p65 phosphorylation. Basal NF-κB activity was also inhibited by Erg overexpression. Chromatin immunoprecipitation showed that Erg binds to the ICAM-1 proximal promoter region, which contains 7 putative ETS binding sites. To test the anti-inflammatory role of Erg in vivo, we used a murine model of TNF-α-dependent acute inflammation. The injection of AdErg into the paw decreased TNF-α-induced inflammation compared with control. Finally, staining of human coronary plaques showed loss of Erg expression from the endothelium overlaying active plaque shoulders.

CONCLUSIONS

We have identified a novel physiological anti-inflammatory pathway under the control of the transcription factor Erg; this pathway inhibits NF-κB-dependent transcription and TNF-α-induced inflammation in vivo. These results suggest a novel approach to anti-inflammatory therapies.

ETS family protein ETV2 is required for initiation of the endothelial lineage but not the hematopoietic lineage in the Xenopus embryo

Transcription factors of the ETS family are important regulators of endothelial and hematopoietic development. We have characterized the Xenopus orthologue of the ETS transcription factor, ETV2. Expression analysis shows that etv2 is highly expressed in hematopoietic and endothelial precursor cells in the Xenopus embryo. In gain-of-function experiments, ETV2 is sufficient to activate ectopic expression of vascular endothelial markers. In addition, ETV2 activated expression of hematopoietic genes representing the myeloid but not the erythroid lineage. Loss-of-function studies indicate that ETV2 is required for expression of all endothelial markers examined. However, knockdown of ETV2 has no detectable effects on expression of either myeloid or erythroid markers. This contrasts with studies in mouse and zebrafish where ETV2 is required for development of the myeloid lineage. Our studies confirm an essential role for ETV2 in endothelial development, but also reveal important differences in hematopoietic development between organisms.

VE-statin/egfl7 expression in endothelial cells is regulated by a distal enhancer and a proximal promoter under the direct control of Erg and GATA-2

Angiogenesis is the process by which new blood vessels arise from existing ones by the budding out of endothelial cell capillaries from the luminal side of blood vessels. Blood vessel formation is essential for organ development during embryogenesis and is associated with several physiological and pathological processes, such as wound healing and tumor development. The VE-statin/egfl7 gene is specifically expressed in endothelial cells during embryonic development and in the adult. We studied here the regulatory mechanisms that control this tissue-specific expression. RT-qPCR analyses showed that the specificity of expression of VE-statin/egfl7 in endothelial cells is not shared with its closest neighbor genes notch1 and agpat2 on the mouse chromosome 2. Chromatin-immunoprecipitation analysis of histone modifications at the VE-statin/egfl7 locus showed that the chromatin is specifically opened in endothelial cells, but not in fibroblasts at the transcription start sites. A 13 kb genomic fragment of promoter was cloned and analyzed by gene reporter assays which showed that two conserved regions are important for the specific expression of VE-statin/egfl7 in endothelial cells; a −8409/−7563 enhancer and the −252/+38 region encompassing the exon-1b transcription start site. The latter contains essential GATA and ETS-binding sites, as assessed by linker-scanning analysis and site-directed mutagenesis. An analysis of expression of the ETS and GATA transcription factors showed that Erg, Fli-1 and GATA-2 are the most highly expressed factors in endothelial cells. Erg and GATA-2 directly control the expression of the endogenous VE-statin/egfl7 while Fli-1 probably exerts an indirect control, as assessed by RNA interference and chromatin immunoprecipitation. This first detailed analysis of the mechanisms that govern the expression of the VE-statin/egfl7 gene in endothelial cells pinpoints the specific importance of ETS and GATA factors in the specific regulation of genes in this cell lineage.

VE-cadherin: at the front, center, and sides of endothelial cell organization and function

Endothelial cells form cell-cell adhesive structures, called adherens and tight junctions, which maintain tissue integrity, but must be dynamic for leukocyte transmigration during the inflammatory response and cellular remodeling during angiogenesis. This review will focus on Vascular Endothelial (VE)-cadherin, an endothelial-specific cell-cell adhesion protein of the adherens junction complex. VE-cadherin plays a key role in endothelial barrier function and angiogenesis, and consequently VE-cadherin availability and function are tightly regulated. VE-cadherin also participates directly and indirectly in intracellular signaling pathways that control cell dynamics and cell cycle progression. Here we highlight recent work that has advanced our understanding of multiple regulatory and signaling mechanisms that converge on VE-cadherin and have consequences for endothelial barrier function and angiogenic remodeling.

ERG oncoprotein expression in prostate cancer: clonal progression of ERG-positive tumor cells and potential for ERG-based stratification

Gene fusions prevalent in prostate cancer (CaP) lead to the elevated expression of the ERG proto-oncogene. ERG activation present in 50–70% of prostate tumors underscores one of the most common oncogenic alterations in CaP. Despite numerous reports of gene fusions and mRNA expression, ERG oncoprotein status in CaP still remains to be defined. Furthermore, development of ERG protein-based assays may provide a new dimension to evaluation of gene fusions involving diverse androgen-regulated promoters and the ERG protein-coding sequence. Through exhaustive evaluations of 132 whole-mount prostates (261 tumor foci and over 200 000 benign glands) for the ERG oncoprotein nuclear expression, we demonstrated 99.9% specificity for detecting prostate tumor cells using a highly specific anti-ERG monoclonal antibody. The ERG oncoprotein expression correlated well with fusion transcript or gene fusion in randomly selected specimens. Strong concordance of ERG-positive foci of prostatic intraepithelial neoplasia (PIN) with ERG-positive carcinoma (82 out of 85 sections with PIN, 96.5%) affirms the biological role of ERG in clonal selection of prostate tumors in 65% (86 out of 132) of patients. Conversely, ERG negative PINs were associated with ERG-negative carcinoma. Taken together, the homogeneous and strong ERG expression detected in individual tumors establishes the potential for ERG oncoprotein-based stratification of CaP.

Tumour angiogenesis is reduced in the Tc1 mouse model of Down's syndrome

Down's syndrome (DS) is a genetic disorder caused by full or partial trisomy of human chromosome 21 and presents with many clinical phenotypes including a reduced incidence of solid tumours. Recent work with the Ts65Dn model of DS, which has orthologues of about 50% of the genes on chromosome 21 (Hsa21), has indicated that three copies of the ETS2 (ref. 3) or DS candidate region 1 (DSCR1) genes (a previously known suppressor of angiogenesis) is sufficient to inhibit tumour growth. Here we use the Tc1 transchromosomic mouse model of DS to dissect the contribution of extra copies of genes on Hsa21 to tumour angiogenesis. This mouse expresses roughly 81% of Hsa21 genes but not the human DSCR1 region. We transplanted B16F0 and Lewis lung carcinoma tumour cells into Tc1 mice and showed that growth of these tumours was substantially reduced compared with wild-type littermate controls. Furthermore, tumour angiogenesis was significantly repressed in Tc1 mice. In particular, in vitro and in vivo angiogenic responses to vascular endothelial growth factor (VEGF) were inhibited. Examination of the genes on the segment of Hsa21 in Tc1 mice identified putative anti-angiogenic genes (ADAMTS1and ERG) and novel endothelial cell-specific genes, never previously shown to be involved in angiogenesis (JAM-B and PTTG1IP), that, when overexpressed, are responsible for inhibiting angiogenic responses to VEGF. Three copies of these genes within the stromal compartment reduced tumour angiogenesis, explaining the reduced tumour growth in DS. Furthermore, we expect that, in addition to the candidate genes that we show to be involved in the repression of angiogenesis, the Tc1 mouse model of DS will permit the identification of other endothelium-specific anti-angiogenic targets relevant to a broad spectrum of cancer patients.

Endothelial Fli1 deficiency impairs vascular homeostasis: a role in scleroderma vasculopathy

Systemic sclerosis or scleroderma (SSc) is a complex autoimmune connective tissue disease characterized by obliterative vasculopathy and tissue fibrosis. The molecular mechanisms underlying SSc vasculopathy are largely unknown. Friend leukemia integration factor 1 (Fli1), an important regulator of immune function and collagen fibrillogenesis, is expressed at reduced levels in endothelial cells in affected skin of patients with SSc. To develop a disease model and to investigate the function of Fli1 in the vasculature, we generated mice with a conditional deletion of Fli1 in endothelial cells (Fli1 CKO). Fli1 CKO mice showed a disorganized dermal vascular network with greatly compromised vessel integrity and markedly increased vessel permeability. We show that Fli1 regulates expression of genes involved in maintaining vascular homeostasis including VE-cadherin, platelet endothelial cell adhesion molecule 1, type IV collagen, matrix metalloproteinase 9, platelet-derived growth factor B, and S1P(1) receptor. Accordingly, Fli1 CKO mice are characterized by down-regulation of VE-cadherin and platelet endothelial cell adhesion molecule 1, impaired development of basement membrane, and a decreased presence of alpha-smooth muscle actin-positive cells in dermal microvessels. This phenotype is consistent with a role of Fli1 as a regulator of vessel maturation and stabilization. Importantly, vascular characteristics of Fli1 CKO mice are recapitulated by SSc microvasculature. Thus, persistently reduced levels of Fli1 in endothelial cells may play a critical role in the development of SSc vasculopathy.

Expression and functional significance of Twist1 in hepatocellular carcinoma: its role in vasculogenic mimicry

The up-regulation and nuclear relocation of epithelial-mesenchymal transition (EMT) regulator Twist1 have been implicated in the tumor invasion and metastasis of human hepatocellular carcinoma (HCC). The term vasculogenic mimicry (VM) refers to the unique capability of aggressive tumor cells to mimic the pattern of embryonic vasculogenic networks. However, the relationship between Twist1 and VM formation is not clear. In this study, we explored HCC as a VM and EMT model in order to investigate the role of Twist1 in VM formation. We first examined the expression of Twist1 in human HCC samples and cell lines and found that Twist1 was frequently overexpressed in the nuclear relocation occurring in VM-positive HCCs (13/18 [72%]). Twist1 nuclear expression was likewise significantly associated with VM formation. Clinicopathological analysis revealed that both VM and Twist1 nuclear expressions present shorter survival durations than those without expression. We consistently demonstrated that an overexpression of Twist1 significantly enhanced cell motility, invasiveness, and VM formation in an HepG2 cell. Conversely, a knockdown of Twist1 by the short hairpin RNA approach remarkably reduced Bel7402 cell migration, invasion, and VM formation. Using chromatin immunoprecipitation, we also showed that Twist1 binds to the vascular endothelial (VE)-cadherin promoter and enhances its activity in a transactivation assay.

CONCLUSION

The results of this study indicate that Twist1 induces HCC cell plasticity in VM cells more through the suppression of E-cadherin expression and the induction of VE-cadherin up-regulation than through the VM pattern in vivo and in a three-dimensional in vitro system. Our findings also demonstrate a novel cogitation in cancer stem-like cell differentiation and that related molecular pathways may be used as novel therapeutic targets for the inhibition of HCC angiogenesis and metastasis.

Noninvasive molecular imaging of apoptosis in vivo using a modified firefly luciferase substrate, Z-DEVD-aminoluciferin

Apoptosis is a highly regulated process of programmed cell death essential for normal physiology. Dysregulation of apoptosis contributes to the development and progression of various diseases, including cancer, neurodegenerative disorders, and chronic heart failure. Quantitative noninvasive imaging of apoptosis in preclinical models would allow for dynamic longitudinal screening of compounds and facilitates a more rapid determination of therapeutic efficacy. In this study, we report the in vivo characterization of Z-DEVD-aminoluciferin, a modified firefly luciferase substrate that in apoptotic cells is cleaved by caspase-3 to liberate aminoluciferin, which can be consumed by luciferase to generate a luminescent signal. In two oncology models, namely SKOV3-luc and MDA-MB-231-luc-LN, at 24, 48, and 72 h after treatment with docetaxel, animals were injected with Z-DEVD-aminoluciferin and bioluminescent images were acquired. Significantly more light was detected at 24 (P<0.05), 48 (P<0.01), and 72 h (P<0.01) in the docetaxel-treated group compared with the vehicle-treated group, with caspase-3 activation at these time points confirmed using immunohistochemistry. Importantly, whereas significant differences between groups were detected as early as 24 h after treatment by molecular imaging, caliper measurements were unable to detect a difference for 4-5 additional days. Taken together, these data show that in vivo imaging of apoptosis using Z-DEVD-aminoluciferin could provide a sensitive and rapid method for early detection of drug efficacy, which could potentially be used by numerous therapeutic programs.

Regulation of angiogenesis by ETS transcription factors

Transcription factors of the ETS family are important regulators of endothelial gene expression. Here, we review the evidence that ETS factors regulate angiogenesis and briefly discuss the target genes and pathways involved. Finally, we discuss novel evidence that shows how these transcription factors act in a combinatorial fashion with others, through composite sites that may be crucial in determining endothelial specificity in gene transcription.

ERG is required for the differentiation of embryonic stem cells along the endothelial lineage

BACKGROUND

The molecular mechanisms that govern stem cell differentiation along the endothelial lineage remain largely unknown. Ets related gene (ERG) has recently been shown to participate in the transcriptional regulation of a number of endothelial specific genes including VE-cadherin (CD144), endoglin, and von Willebrand's Factor (vWF). The specific role of the ETS factor ERG during endothelial differentiation has not been evaluated.

RESULTS

ERG expression and function were evaluated during the differentiation of embryonic stem cells into embryoid bodies (EB). The results of our study demonstrate that ERG is first expressed in a subpopulation of vascular endothelial growth factor receptor 2 (VEGF-R2) expressing cells that also express VE-cadherin. During ES cell differentiation, ERG expression remains restricted to cells of the endothelial lineage that eventually coalesce into primitive vascular structures within embryoid bodies. ERG also exhibits an endothelial cell (EC)-restricted pattern during embryogenesis. To further define the role of ERG during ES cell differentiation, we used a knockdown strategy to inhibit ERG expression. Delivery of three independent shRNA led to 70-85% reductions in ERG expression during ES cell differentiation compared to no change with control shRNA. ERG knockdown was associated with a marked reduction in the number of ECs, the expression of EC-restricted genes, and the formation of vascular structures.

CONCLUSION

The ETS factor ERG appears to be a critical regulator of EC differentiation.

Vascular integrity mediated by vascular endothelial cadherin and regulated by sphingosine 1-phosphate and angiopoietin-1

Development of blood vessels is coordinated by angiogenesis and stabilization of vascular endothelial cells (ECs). The vascular network is established during embryogenesis to supply oxygen and nutrients to the tissues and organs. However, after cardiac or peripheral ischemia is caused by occlusion of the vessels, new vessels must be formed to rescue the ischemic tissues. Many angiogenic growth factors and chemokines are produced in the ischemic tissue to induce angiogenic sprouting of preexisting vessels. Branched vessels must be again restabilized to form mature vessels that deliver blood to the tissues. To this end, vascular EC-cell adhesion is tightly regulated by cell-cell adhesion molecules and extracellular stimuli that activate G protein-coupled receptors and receptor tyrosine kinases exclusively expressed on vascular ECs. This review spotlights the recent studies of vascular endothelial cadherin and of sphingosine 1-phosphate signaling and angiopoietin-Tie signaling.

ERG expression is an independent prognostic factor and allows refined risk stratification in cytogenetically normal acute myeloid leukemia: a comprehensive analysis of ERG, MN1, and BAALC transcript levels using oligonucleotide microarrays

PURPOSE

Recently, several novel molecular prognostic markers were identified in cytogenetically normal acute myeloid leukemia (CN-AML). In addition to the well-known influence of FLT3, NPM1, and CEBPA mutations, high transcript levels of the ERG, BAALC, and MN1 genes have been associated with inferior outcomes, but the relative importance of these risk markers remains to be defined.

PATIENTS AND METHODS

We analyzed ERG, BAALC, and MN1 expression levels in a cohort of 210 patients with CN-AML who received intensive chemotherapy. Expression levels of ERG, BAALC, and MN1 were determined in bone marrow samples by using oligonucleotide microarrays.

RESULTS

High transcript levels of ERG, BAALC, and MN1 were predictors for inferior overall survival (OS) and a lower rate of complete remissions (CRs). There were significant positive correlations between the expression levels of all three genes. ERG expression levels predicted OS in elderly patients (ie, age 60 years or older) with CN-AML (P = .006) as well as in younger patients (P = .013). In multivariate analyses, high ERG expression was independently associated with a lower CR rate (P = .013), shorter event-free survival (P = .008), and shorter OS (P = .005). Patients who had low ERG levels and absent FLT3 internal tandem duplication (ITD) had a 5-year OS of 44%, and patients who had high ERG expression and FLT3 ITD had a 5-year OS of only 5%.

CONCLUSION

We analyzed a comprehensive set of molecular risk factors in a large, homogeneous CN-AML patient cohort. In this study, high ERG expression levels emerged as a strong negative prognostic factor and provided prognostic information in addition to established molecular markers.

[Genes that make the endothelial identity]

The endothelium is a tissue with a distinct identity due to the specific expression of molecular markers by endothelial cells. Further, the endothelium displays a structural heterogeneity illustrated by the expression of specific markers in arteries and in veins. Here, we present a review of the transcriptional and epigenetic mechanisms regulating the expression of the main markers of endothelial cells in man and mouse, demonstrating that there is no common and unique mechanism of specific expression of genes in these cells.

[The bHLH TAL1 protein: a key molecule in the hematopoietic and endothelial systems]

The formation of blood cells and vascular networks occurs simultaneously during development, and both lineages remain in close association in all adult tissues. The functional setting of both systems within the embryo and their renewal during adult life are highly complex processes, and require the involvement of numerous molecular actors, the activities of which are often overlapping. Here, I review the activity of TAL-1, a basic-helix-loop-helix transcription factor, which plays a key role in the formation and functioning of both blood and endothelial systems, with a particular emphasis on recent data that associate TAL-1 with angiogenesis.

Alterations in transcriptional responses associated with vascular aging

Vascular aging is an independent risk factor for cardiovascular disease that can occur in the absence of other traditional risk factors. Inflammation is a hallmark of vascular aging that ultimately leads to structural changes in the vessel wall including an increase in medial thickness and perivascular fibrosis. Several classes of transcription factors have been identified that participate in the regulation of cellular responses associated with vascular aging. Nuclear factor (NF)-κB is the prototypic example of a transcriptional activator in the setting of inflammation, being activated in response to multiple inflammatory mediators including pro-inflammatory cytokines and bacterial endotoxin. In contrast, the activation of the nuclear hormone receptor and transcription factor peroxisome proliferator-activated receptor-alpha (PPAR-α) results in its translocation from the cell surface to the nucleus where it exerts anti-inflammatory effects. Vascular aging is also associated with endothelial dysfunction. One important repair mechanism for improving endothelial function is the recruitment of endothelial progenitor cells (EPCs). In the setting of aging the number of EPCs diminishes which has been linked to a decrease in the activity and/or expression of the transcription factor hypoxia inducible factor (HIF)-1 alpha. A change in the balance of the activity of pro-inflammatory transcription factors versus those that inhibit inflammation likely contributes to the process of vascular aging. The purpose of this review is to summarize our current knowledge of these age-related changes in transcriptional responses, and to discuss the therapeutic potential of targeting some of these factors.

Inhibition of endothelial cell apoptosis by netrin-1 during angiogenesis

Netrin-1 was recently proposed to play an important role in embryonic and pathological angiogenesis. However, data reported led to the apparently contradictory conclusions that netrin-1 is either a pro- or an antiangiogenic factor. Here, we reconcile these opposing observations by demonstrating that netrin-1 acts as a survival factor for endothelial cells, blocking the proapoptotic effect of the dependence receptor UNC5B and its downstream death signaling effector, the serine/threonine kinase DAPK. The netrin-1 effect on blood vessel development is mimicked by caspase inhibitors in ex vivo assays, and the inhibition of caspase activity, the silencing of the UNC5B receptor, and the silencing of DAPK are each sufficient to rescue the vascular sprouting defects induced by netrin-1 silencing in zebrafish. Thus, the proapoptotic effect of unbound UNC5B and the survival effect of netrin-1 on endothelial cells finely tune the angiogenic process.

Antiinflammatory effects of the ETS factor ERG in endothelial cells are mediated through transcriptional repression of the interleukin-8 gene

ERG (Ets-related gene) is an ETS transcription factor that has recently been shown to regulate a number of endothelial cell (EC)-restricted genes including VE-cadherin, von Willebrand factor, endoglin, and intercellular adhesion molecule-2. Our preliminary data demonstrate that unlike other ETS factors, ERG exhibits a highly EC-restricted pattern of expression in cultured primary cells and several adult mouse tissues including the heart, lung, and brain. In response to inflammatory stimuli, such as tumor necrosis factor-alpha, we observed a marked reduction of ERG expression in ECs. To further define the role of ERG in the regulation of normal EC function, we used RNA interference to knock down ERG. Microarray analysis of RNA derived from ERG small interfering RNA- or tumor necrosis factor-alpha-treated human umbilical vein (HUV)ECs revealed significant overlap (P<0.01) in the genes that are up- or downregulated. Of particular interest to us was a significant change in expression of interleukin (IL)-8 at both protein and RNA levels. Exposure of ECs to tumor necrosis factor-alpha is known to be associated with increased neutrophil attachment. We observed that knockdown of ERG in HUVECs is similarly associated with increased neutrophil attachment compared to control small interfering RNA-treated cells. This enhanced adhesion could be blocked with IL-8 neutralizing or IL-8 receptor blocking antibodies. ERG can inhibit the activity of the IL-8 promoter in a dose dependent manner. Direct binding of ERG to the IL-8 promoter in ECs was confirmed by chromatin immunoprecipitation. In summary, our findings support a role for ERG in promoting antiinflammatory effects in ECs through repression of inflammatory genes such as IL-8.

Transcription and splicing regulation in human umbilical vein endothelial cells under hypoxic stress conditions by exon array

Background

The balance between endothelial cell survival and apoptosis during stress is an important cellular process for vessel integrity and vascular homeostasis, and it is also pivotal in angiogenesis during the development of many vascular diseases. However, the underlying molecular mechanisms remain largely unknown. Although both transcription and alternative splicing are important in regulating gene expression in endothelial cells under stress, the regulatory mechanisms underlying this state and their interactions have not yet been studied on a genome-wide basis.

Results

Human umbilical vein endothelial cells (HUVECs) were treated with cobalt chloride (CoCl₂) both to mimic hypoxia and to induce cell apoptosis and alternative splicing responses. Cell apoptosis rate analysis indicated that HUVECs exposed to 300 μM CoCl₂ for 24 hrs were initially counterbalancing apoptosis with cell survival. We therefore used the Affymetrix exon array system to determine genome-wide transcript- and exon-level differential expression. Other than 1583 differentially expressed transcripts, 342 alternatively spliced exons were detected and classified by different splicing types. Sixteen alternatively spliced exons were validated by RT-PCR. Furthermore, direct evidence for the ongoing balance between HUVEC survival and apoptosis was provided by Gene Ontology (GO) and protein function, as well as protein domain and pathway enrichment analyses of the differentially expressed transcripts. Importantly, a novel molecular module, in which the heat shock protein (HSP) families play a significant role, was found to be activated under mimicked hypoxia conditions. In addition, 46% of the transcripts containing stress-modulated exons were differentially expressed, indicating the possibility of combinatorial regulation of transcription and splicing.

Conclusion

The exon array system effectively profiles gene expression and splicing on the genome-wide scale. Based on this approach, our data suggest that transcription and splicing not only regulate gene expression, but also carry out combinational regulation of the balance between survival and apoptosis of HUVECs under mimicked hypoxia conditions. Since cell survival following the apoptotic challenge is pivotal in angiogenesis during the development of many vascular diseases, our results may advance the knowledge of multilevel gene regulation in endothelial cells under physiological and pathological conditions.

Transcriptional control of endothelial cell development

The transcription factors that regulate endothelial cell development have been a focus of active research for several years, and many players in the endothelial transcriptional program have been identified. This review discusses the function of several major regulators of endothelial transcription, including members of the Sox, Ets, Forkhead, GATA, and Kruppel-like families. This review also highlights recent developments aimed at unraveling the combinatorial mechanisms and transcription factor interactions that regulate endothelial cell specification and differentiation during vasculogenesis and angiogenesis.